A (usually) flat, circular recording medium whose data-bearing surface is exposed and is not enclosed within a protective housing; typically used to refer to optical recording media such as CDs, DVDs, LaserDiscs, the magnetic media in Floppy Disks, etc.

A recording medium where a disc is enclosed — either permanently or not — within a protective housing, cartridge, casing, or other external structure; the term may encompass magnetic, optical, magneto-optical, and other recording technologies.

Any of a number of data storage formats that consists of an optical disc enclosed in a protective cartridge.